The hallmark of autoimmune disease is the accumulation of T cell in lymphoid organs and in target tissues such as long, liver, kidney, CNS, bowel, skin or synovial tissue. Current tissues are limited to the analysis of these sites using animal models at a single time point or in humans using limited tissue samples and usually at a late stage of disease. Therefore, it is difficult to quantitate the kinetics of T cell production and migration at lymphoid and non-lymphoid sites. Also, mice must be sacrificed to analyze T cells at different sites, and such studies are not feasible in human subjects. The present proposal to analyze auto-reactive T cells in vivo is made possible by three new developments in our laboratory. 1) We have developed the Db/HY TCR transgenic mouse transfer model using SCID recipients that develop autoimmune disease. This will enable analysis of production, elimination and migration of autoimmune T cells from the earliest time point after transfer and through the lifetime of the recipient mice. 2) These T cells can be induced to express the human type II somatostatin receptor delivered by a T cell tropic adeno-associated virus (AAV CMV Hsstr2 mPV). This will enable high expression of the unique hSSTR2 receptor on all transfer T cells that can be recognized at later time points after transfer with a low molecular weight tracer. 3) We have developed a whole-mouse body reference device that enable precise correlation between highly sensitive nuclear imaging and high resolution MRI imaging. This enables construction of a nuclear-MRI fusion image that enables precise identification of tissue sites containing auto-reactive T cells. This aspect of the proposal will utilize the unique nuclear imaging facility and the 4.7 T MRI facility to image the same mouse by both methods and at different time points after T cell transfer. Specific Aims include: 1) Determine optimal T cell transfer technology and imaging technology using the Db/HY TCR transfer model applicable to lymphoid and non-lymphoid organs. 2) Determine if AAV including the human type II somatostatin receptor can be used to image T cell production and migration after transfer. 3) Utilize the mouse whole-body reference to correlate high resolution 4.7 T MRI images with high sensitivity nuclear medicine images. 4) Determine if these techniques will enable analysis of human T cells from patients with autoimmune diseases after transfer to SCID mice. The results of these experiments will apply new imaging technologies to study auto-reactive T cells in vivo. These results should pave the way for studies of human lymphocytes by labeling in vivo to determine the spacial and temporal production of the immune response leading to systemic autoimmune diseases.